THE DECISION by Attorney General Janet Reno and FBI Director Louis Freeh to broaden the Chinese nuclear spying investigation contains an implicit repudiation of the manner in which the bureau's investigation up until now has taken place. This is welcome, as everything that has become public about this investigation suggests that it was flawed from the beginning -- so flawed that we may never know the extent to which China has acquired American nuclear secrets through espionage or who its agents in that acquisition may have been.

The decision in effect to start over is at first a reevaluation of the seemingly capricious judgment by Energy Department investigators that the compromise of the W-88 warhead design came from Los Alamos, though many people elsewhere apparently had access to the information. It is, likewise, an admission that investigators may have prematurely focused on one person at Los Alamos, scientist Wen Ho Lee. And it is an admission by the bureau that it should not have adopted so blithely the premises handed to it by a flawed Energy Department review.

Once the FBI had the matter, moreover, it moved prematurely to conduct electronic surveillance against Mr. Lee, though the evidence against him was quite weak and though other investigative avenues were plainly available. When the Justice Department squelched this surveillance request, the bureau did not gather more evidence and try again. In other words, the investigation seems to have focused too narrowly on one person at one lab and proceeded incompetently against him.

It's hard to overestimate the consequences of the failure here. A better investigation may well have identified actual Chinese agents rather than publicly tarring a man with accusations of espionage who cannot be indicted for it and who could be innocent. Even had the investigation against Mr. Lee proceeded differently, we would know a great deal more about his conduct than we currently do.

What we have now is the worst of all worlds: A publicly fingered suspect whom we cannot fairly evaluate, a giant unanswered question regarding the scope and extent of Chinese nuclear espionage, and no particular prospects of answering that question. Expanding this investigation is a move that should have been taken long ago. Surely law enforcement can do better this time.